1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, it relates to an electron beam writing apparatus for writing a pattern onto a target workpiece by using a variable shaped electron beam, and to a method thereof.
2. Description of Related Art
The microlithography technique which advances microminiaturization of semiconductor devices is extremely important as being the unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with the high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. Then, in order to form a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is needed. The electron beam writing technique intrinsically having excellent resolution is used for producing such a highly precise master pattern.
FIG. 58 is a schematic diagram for explaining operations of a conventional variable-shaped electron beam (EB) writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus operates as follows: A first aperture plate 410 has a quadrangular such as rectangular opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 that passed through the opening 411 into a desired rectangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shaped opening 421 and thereby to irradiate a target workpiece or “sample” 340 mounted on a stage which continuously moves in one predetermined direction (e.g. x direction) during writing or “drawing”. In other words, a rectangle shaped as a result of passing through both the opening 411 and the variable-shaped opening 421 is written in the writing region of the target workpiece 340 on the stage. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is referred to as a VSB (Variable Shaped Beam) method.
When a target workpiece, such as a mask, to which a resist film is applied, is irradiated by an electron beam, the irradiated position and its periphery may have been charged with the electron beam previously irradiated. The position displacement caused by this charging phenomenon has not been conventionally regarded as a problem in the variable-shaped type electron beam pattern writing apparatus. However, with the pattern miniaturization as mentioned above, such position displacement due to the charging phenomenon has become a problem. In particular, improvement of the pattern position accuracy of photomasks is required more than ever because of introducing a double patterning technique.
Conventionally, as a method for correcting a position displacement of the position irradiated by the beam, there has been known to form a charge dissipation layer (CDL) on a resist layer in order to prevent charging of the resist surface. However, since the charge dissipation layer basically has acid property, it has a poor affinity for a chemically amplified resist. Further, there is a need to provide new equipment in order to form the charge dissipation layer, thereby increasing the manufacturing cost of a photomask. For this reason, it is desired to perform charging effect correction (CEC) without using the charge dissipation layer.
With regard to a position displacement correction amount caused by charging, there is proposed a writing apparatus which calculates a correction amount of position displacement of a beam irradiation position, based on an electric field strength and applies a beam based on the correction amount (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2007-324175). According to such a writing apparatus, a position displacement amount distribution is calculated from an irradiation amount (exposure) distribution through a linear response function assuming that there exists a linearly proportional relationship between the irradiation amount distribution and a charge amount distribution.
With regard to irradiation position displacement due to the charging phenomenon, it has been found according to the examination carried out by the inventors that there exist position displacement caused by charge which does not change temporally and position displacement caused by charge which decays as time passes. Particularly, when focusing on the latter position displacement resulting from charge which decays with time, a problem inevitably arises in that a processing time equivalent to the decay time is required for the writing operation itself for measuring the charge amount temporal decay as an essential restriction when estimating the charge amount on the resist surface in the pattern writing. Under such a restriction, there are needed a method of measuring the temporal decay more simply and quantifying it and a method of correcting position displacement with using the quantification result. However, conventionally, the method of correcting position displacement resulting from electric charge decay has not been sufficiently established.